Method and system of osnr-sensing spectrum allocation with optical channel performance guarantee

ABSTRACT

The present invention provides a method and system of OSNR-sensing spectrum allocation with optical channel performance guarantee. The method includes constructing an OSNR evaluation model; acquiring the shortest path between a source node and a destination node; acquiring a plurality of modulation formats and corresponding thresholds, sorting the plurality of modulation formats in descending order, and acquiring a list of the sorted modulation formats; calculating the bandwidth required by the lightpath service based on the bandwidth demand and FEC overhead by using the modulation format with the highest spectrum efficiency; substituting the bandwidth required by the lightpath service into the OSNR evaluation model and obtaining the number of FS actually required by the service; and allocating the spectrum resource required by the current service to the shortest path by using a first-fit algorithm and obtaining the center frequency of the current service on the lightpath.

FIELD OF THE INVENTION

The present invention relates to the technical field of opticalcommunication, and more particularly to a method and system ofOSNR-sensing spectrum allocation with optical channel performanceguarantee.

DESCRIPTION OF THE RELATED ART

For an optical transmission system, characteristics such as low loss andlarge effective area of the optical fiber contribute to improvement inperformance. However, from the perspective of optical fibermanufactures, it is very challenging and costly to fabricate an opticalfiber with a low attenuation coefficient and a large effective area. Asdisclosed in the document “Spectrum efficiency and cost evaluation forG.654.E fiber . . . ,” N. Guo et al., in Proc. ACP 2020, paper M4A.274,the spectrum efficiency increases slowly as the attenuation coefficientof the optical fiber decreases, and increases rapidly as the effectivearea of the optical fiber increases from 83 μm² to 130 μm² in apoint-to-point optical transmission system.

However, in real life, the optical fiber provides lightpath service tothe network. Therefore, considering a complete network topology, theresult from a point-to-point system cannot accurately reflect theadvantages for optical signal transmission in the network introduced byan optical fiber with low loss and large effective area, and thetraditional optical signal-to-noise ratio evaluation model is no longeraccurate.

SUMMARY OF THE INVENTION

In view of this, the present invention aims to solve the technicalproblem in the prior art that for a complete network topology, theresult from a point-to-point system cannot accurately reflect theadvantages for optical signal transmission in the network introduced byan optical fiber with low loss and large effective area, and thetraditional optical signal-to-noise ratio evaluation model is no longeraccurate.

To solve the above technical problem, the present invention provides amethod of OSNR-sensing spectrum allocation with optical channelperformance guarantee, including the following steps:

-   -   S1: constructing an OSNR evaluation model to evaluate signal        transmission quality of the lightpath, the OSNR evaluation model        including amplified spontaneous emission noise, nonlinear        interference and filter narrowing effect due to ROADM cascading;    -   S2: sending a lightpath service request and acquiring the        shortest path between the source node and the destination node;    -   S3: acquiring a plurality of modulation formats and        corresponding thresholds, sorting the plurality of modulation        formats according to their spectrum efficiencies in descending        order, and obtaining a list of the sorted modulation formats;    -   S4: calculating the bandwidth required by the lightpath service        based on the bandwidth demand and FEC overhead by using the        modulation format with the highest spectrum efficiency;    -   S5: substituting the bandwidth required by the lightpath service        into the OSNR evaluation model and obtaining the number of FS        actually required by the service; and    -   S6: allocating the spectrum resource required by the current        service to the shortest path by using the first-fit algorithm        and obtaining the center frequency of the current service on the        lightpath.

Preferably, the method includes, after step of allocating the spectrumresource required by the current service to the shortest path by usingthe first-fit algorithm and obtaining the center frequency of thecurrent service on the lightpath:

-   -   evaluating the OSNR quality by using a full-spectrum loading        strategy, a margin reservation strategy and a spectrum-dependent        strategy respectively to guarantee the optimum optical channel        performance after spectrum allocation.

Preferably, evaluating the OSNR quality by using the full-spectrumloading strategy includes:

-   -   evaluating the transmission quality (i.e., OSNR) of the        lightpath when all the spectrum resources on the link are        occupied and the OSNR performance is the worst;    -   if OSNR satisfies the threshold for the current modulation        format, establishing a lightpath and ending the allocation        process, otherwise, calculating the bandwidth required by the        lightpath service based on the bandwidth demand and the FEC        overhead by using the modulation format subsequent to the        current modulation format in the modulation format list, and        repeating S5 and the steps thereafter until the lightpath        service request is established; and    -   after all the lightpath service requests have been successfully        established, checking all the lightpath service requests in        consideration of the nonlinear interference, recalculating the        OSNR and determining whether it still satisfies the selected        modulation format, and if it does not satisfy the current        modulation format, blocking this service.

Preferably, evaluating the OSNR quality by using the margin reservationstrategy includes:

-   -   calculating the transmission quality OSNR of the lightpath based        on the center frequency of the current spectrum resource on the        fiber link;    -   reserving a margin M;    -   if (OSNR-M) satisfies the threshold for the current modulation        format, establishing a lightpath and ending the allocation        process, otherwise, calculating the bandwidth required by the        lightpath service based on the bandwidth demand and the FEC        overhead by using the modulation format subsequent to the        current modulation format in the modulation format list, and        repeating S5 and the steps thereafter until the lightpath        service request is established; and    -   after all the lightpath service requests have been successfully        established, checking all the lightpath service requests in        consideration of the nonlinear interference, recalculating the        OSNR and determining whether it still satisfies the selected        modulation format, and if it does not satisfy the current        modulation format, blocking this service.

Preferably, evaluating the OSNR quality by using the spectrum-dependentstrategy includes:

-   -   calculating the transmission quality OSNR of the lightpath based        on the center frequency of the current spectrum resource on the        fiber link;    -   if the OSNR satisfies the threshold for the current modulation        format, establishing a lightpath and ending the allocation        process, otherwise, calculating the bandwidth required by the        lightpath service based on the bandwidth demand and the FEC        overhead by using the modulation format subsequent to the        current modulation format in the modulation format list, and        repeating S5 and the steps thereafter until the lightpath        service request is established; and after all the lightpath        service requests have been successfully established, checking        all the lightpath service requests in consideration of the        nonlinear interference, recalculating the OSNR and determining        whether it still satisfies the current modulation format;    -   if the OSNR does not satisfy the current modulation format,        releasing the spectrum resource used by all the lightpaths that        have not been checked starting from the failed lightpath; and    -   for the failed service request, lowering the level of the        modulation format used and reallocating the spectrum along the        same shortest path.

Preferably, the method further includes, after the step of, for thefailed service request, lowering the level of the modulation format usedand reallocating the spectrum along the same shortest path:

-   -   for a lightpath that has not been checked, reallocating the        spectrum by using the modulation format that has been previously        used and checking whether this lightpath satisfies the        signal-to-noise ratio requirement; and    -   repeating the process above until all the new lightpaths have        been successfully established and all the lightpaths satisfy the        signal-to-noise ratio requirement.

Preferably, the step S1 includes:

-   -   when the signal bandwidth is BW_(s), the 3 dB bandwidth of the        filter is:

$\begin{matrix}{{{BW}_{3{dB}} = {{BW}_{s} \times \left\lbrack \frac{T\lbrack{dB}\rbrack}{10 \times \left( {- {\ln z}} \right) \times {\log_{10}(\theta)} \times N_{f}} \right\rbrack^{- \frac{1}{2n}}}},} & (1)\end{matrix}$

where T is the insertion loss of the filter in the unit of dB, N_(f) isthe number of cascaded filters, and n is the order of Gaussian function;

-   -   the overall signal-to-noise ratio of the lightpath        OSNR_(lightpath) is:

$\begin{matrix}{{{OSNR}_{lightpath} = \frac{P_{in}}{P_{ASE} + P_{NLI}}},} & (2)\end{matrix}$

-   -   where P_(in) is the transmit power of the lightpath, P_(ASE) is        the power of the ASE noise, and P_(NLI) is the power of NLI        interference;    -   in the case where each optical amplifier can exactly compensate        for the loss of the previous signal, P_(ASE) is calculated by        the formula:

P _(ASE) =F×h×(G−1)×f ₁ ×B ₁  (3)

-   -   where F is the noise figure of the optical amplifier, h is the        Planck constant, G is the gain of the optical amplifier, f_(i)        is the center frequency of the signal, and B_(i) is the        bandwidth of the signal;    -   for the nonlinear interference and assuming additive Gaussian        noise, P_(NLI) can be calculated as:

$\begin{matrix} & (4)\end{matrix}$$P_{NLI} = {{\eta \times P_{ch}^{3}} = {P_{ch}^{3} \times \frac{4}{27} \times \frac{\gamma^{2}L_{eff}^{2}B_{i}}{{\pi(a)}^{- 1}\beta_{2}{R_{5}}^{3}}{\sum_{n = 1}^{N_{ch}}\left\{ {{{asinh}\left\lbrack {{\pi^{2}(a)}^{- 1}\beta_{2}{B_{i}\left( {f_{n} - f_{i} + \frac{B_{n}}{2}} \right)}} \right\rbrack} - {{asinh}\left\lbrack {{\pi^{2}(a)}^{- 1}\beta_{2}{B_{i}\left( {f_{n} - f_{i} - \frac{B_{n}}{2}} \right)}} \right\rbrack}} \right\}}}}$

-   -   where L_(eff)=(1−e^(−α·L) ^(span) )/α·γ=2π×n₂/(λ×A_(eff)),        “asinh” is the inverse hyperbolic sine function, α is the        attenuation coefficient of the optical fiber, β₂ is the second        order fiber dispersion coefficient, L_(span) is the span length,        span meaning the physical link between two adjacent optical        amplifiers, λ is the wavelength of the signal, n₂ is the        nonlinear refractive index of the optical fiber, and A_(eff) is        the effective area of the optical fiber.

Preferably, the plurality of modulation formats in the step S3 includes:PM-64QAM, PM-32QAM, PM-16QAM, PM-8QAM, PM-QPSK and PM-BPSK.

The present invention discloses a system of OSNR-sensing spectrumallocation with optical channel performance guarantee, including:

-   -   an OSNR construction module configured to construct an OSNR        evaluation model to evaluate the signal transmission quality of        the lightpath, the OSNR evaluation model including amplified        spontaneous emission noise, nonlinear interference and filter        narrowing effect due to ROADM cascading;    -   a shortest-path acquisition module configured to send a        lightpath service request and acquire the shortest path between        the source node and the destination node;    -   a modulation format sorting module configured to acquire a        plurality of modulation formats and corresponding thresholds,        sort the plurality of modulation formats according to their        spectrum efficiencies in descending order, and acquire a list of        the sorted modulation formats; and    -   a spectrum allocation module configured to calculate the        bandwidth required by the lightpath service based on the        bandwidth demand and FEC overhead by using the modulation format        with the highest spectrum efficiency; substitute the bandwidth        required by the lightpath service into the OSNR evaluation model        and obtain the number of FS actually required by the service;        and allocate the spectrum resource required by the current        service to the shortest path by using the first-fit algorithm        and acquire the center frequency of the current service on the        lightpath.

Preferably, the system further includes:

-   -   an OSNR quality evaluation module configured to evaluate the        OSNR quality by using a full-spectrum loading strategy, a margin        reservation strategy and a spectrum-dependent strategy        respectively to guarantee the optimum optical channel        performance after spectrum allocation.

Compared with prior art, the technical solution of the present inventionhas the following advantages.

1. The present invention proposes a complete lightpath signal-to-noiseRatio (OSNR) evaluation model on the basis of the traditional GaussianNoise (GN) model in consideration of the cascading effect of theReconfigurable Optical Add-Drop Multiplexer (ROADM).

2. The present invention proposes three spectrum allocation solutions inconsideration of the Cross Channel Interference (XCI) between thelightpath previously established and the lightpath currently to beestablished. Simulation results show that the spectrum-dependentstrategy proposed is the most effective, since spectrum allocationaccording to this strategy considers the current XCI value for each ofthe lightpaths.

3. According to the present invention, in contrast to the traditionalconcept, it is found that although reducing the optical fiber lossalways contributes to increased spectrum efficiency, further increase inthe effective area can no longer substantially increase the spectrumefficiency once the effective area is over 110 μm². This fact is veryimportant for guidance in using optical fibers with low loss and largeeffective area in EON.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a method of OSNR-sensing spectrum allocation with opticalchannel performance guarantee;

FIG. 2 is an exemplary diagram of the spectrum resource of thelightpath;

FIG. 3 is a test network diagram;

FIG. 4 is a diagram of performance comparison between OSNR performanceguarantee strategies; and

FIG. 5 is a diagram of performance comparison between different types ofoptical fibers, in which (a) shows NSFNET and (b) shows USNET.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be further explained with reference to thedrawings and particular embodiments below to enable those skilled in theart to better understand and implement the present invention, but theembodiments listed are not intended as limitations of the presentinvention.

Referring to FIG. 1 , the present invention discloses a method ofOSNR-sensing spectrum allocation with optical channel performanceguarantee including the following steps.

Step 1: constructing an OSNR evaluation model to evaluate signaltransmission quality of the lightpath, the OSNR evaluation modelincluding amplified spontaneous emission noise, nonlinear interferenceand filter narrowing effect due to ROADM cascading, specificallyincluding:

-   -   when the signal bandwidth is BW_(s), the 3 dB bandwidth of the        filter is:

$\begin{matrix}{{{BW}_{3{dB}} = {{BW}_{s} \times \left\lbrack \frac{T\lbrack{dB}\rbrack}{10 \times \left( {- {\ln z}} \right) \times {\log_{10}(\theta)} \times N_{f}} \right\rbrack^{- \frac{1}{2n}}}},} & (1)\end{matrix}$

-   -   where T is the insertion loss of the filter in the unit of dB,        N_(f) is the number of cascaded filters, and n is the order of        Gaussian function;    -   the overall signal-to-noise ratio of the lightpath        OSNR_(lightpath) is:

$\begin{matrix}{{{OSNR}_{lightpath} = \frac{P_{in}}{P_{ASE} + P_{NLI}}},} & (2)\end{matrix}$

-   -   where P_(in) is the transmit power of the lightpath, P_(ASE) is        the power of the ASE noise, and P_(NLI) is the power of NLI        interference;    -   in the case where each optical amplifier can exactly compensate        for the loss of the previous signal, P_(ASE) is calculated by        the formula:

P _(ASE) =F×h×(G−1)×f _(i) ×B _(i)  (3)

-   -   where F is the noise figure of the optical amplifier, h is the        Planck constant, G is the gain of the optical amplifier, f_(i)        is the center frequency of the signal, and B_(i) is the        bandwidth of the signal;    -   for the nonlinear interference and assuming additive Gaussian        noise, P_(NLI) can be calculated as:

$\begin{matrix} & (4)\end{matrix}$$P_{NLI} = {{\eta \times P_{ch}^{3}} = {P_{ch}^{3} \times \frac{4}{27} \times \frac{\gamma^{2}L_{eff}^{2}B_{i}}{{\pi(a)}^{- 1}\beta_{2}{R_{5}}^{3}}{\sum_{n = 1}^{N_{ch}}\left\{ {{{asinh}\left\lbrack {{\pi^{2}(a)}^{- 1}\beta_{2}{B_{i}\left( {f_{n} - f_{i} + \frac{B_{n}}{2}} \right)}} \right\rbrack} - {{asinh}\left\lbrack {{\pi^{2}(a)}^{- 1}\beta_{2}{B_{i}\left( {f_{n} - f_{i} - \frac{B_{n}}{2}} \right)}} \right\rbrack}} \right\}}}}$

-   -   where L_(eff)=(1−e^(−α·L) ^(span) )/α·γ=2π×n₂/(λ×A_(eff)),        “asinh” is the inverse hyperbolic sine function, α is the        attenuation coefficient of the optical fiber, β₂ is the second        order fiber dispersion coefficient, L_(span) is the span length,        span meaning the physical link between two adjacent optical        amplifiers, λ is the wavelength of the signal, n₂ is the        nonlinear refractive index of the optical fiber, and A_(eff) is        the effective area of the optical fiber.

Step 2: sending a lightpath service request and acquiring the shortestpath between the source node and the destination node.

Step 3: acquiring a plurality of modulation formats and correspondingthresholds, sorting the plurality of modulation formats according totheir spectrum efficiencies in descending order, and acquiring a list ofthe sorted modulation formats. The plurality of modulation formats inthe step 3 includes PM-64QAM, PM-32QAM, PM-16QAM, PM-8QAM, PM-QPSK andPM-BPSK.

Step 4: calculating the bandwidth required by the lightpath servicebased on the bandwidth demand and FEC overhead by using the modulationformat with the highest spectrum efficiency.

Step 5: substituting the bandwidth required by the lightpath serviceinto the OSNR evaluation model and obtaining the number of FS actuallyrequired by the service.

Step 6: allocating the spectrum resource required by the current serviceto the shortest path by using the first-fit algorithm, and obtaining thecenter frequency of the current service on the lightpath.

Step 7: evaluating the OSNR quality by using a full-spectrum loadingstrategy, a margin reservation strategy and a spectrum-dependentstrategy respectively to guarantee the optimum optical channelperformance after spectrum allocation.

-   -   (1) Evaluating the OSNR quality by using the full-spectrum        loading strategy includes:    -   evaluating the transmission quality OSNR of the lightpath when        all the spectrum resources on the link are occupied and the OSNR        performance is the worst;    -   if OSNR satisfies the threshold for the current modulation        format, establishing a lightpath and ending the allocation        process; otherwise, calculating the bandwidth required by the        lightpath service based on the bandwidth demand and the FEC        overhead by using the modulation format subsequent to the        current modulation format in the modulation format list, and        repeating S5 and the steps thereafter until the lightpath        service request is established; and    -   after all the lightpath service requests have been successfully        established, checking all the lightpath service requests in        consideration of the nonlinear interference, recalculating the        OSNR and determining whether it still satisfies the selected        modulation format, and if it does not satisfy the current        modulation format, blocking this service.    -   (2) Evaluating the OSNR quality by using the margin reservation        strategy includes:    -   calculating the transmission quality OSNR of the lightpath based        on the center frequency of the current spectrum resource on the        fiber link;    -   reserving a margin M;    -   if (OSNR-M) satisfies the threshold for the current modulation        format, establishing a lightpath and ending the allocation        process, otherwise, calculating the bandwidth required by the        lightpath service based on the bandwidth demand and the FEC        overhead by using the modulation format subsequent to the        current modulation format in the modulation format list, and        repeating S5 and the steps thereafter until the lightpath        service request is established; and    -   after all the lightpath service requests have been successfully        established, checking all the lightpath service requests in        consideration of the nonlinear interference, recalculating the        OSNR and determining whether it still satisfies the selected        modulation format, and if it does not satisfy the current        modulation format, blocking this service.    -   (3) Evaluating the OSNR quality by using the spectrum-dependent        strategy includes:    -   calculating the transmission quality OSNR of the lightpath based        on the center frequency of the current spectrum resource on the        fiber link;    -   if the OSNR satisfies the threshold for the current modulation        format, establishing a lightpath and ending the allocation        process, otherwise, calculating the bandwidth required by the        lightpath service based on the bandwidth demand and the FEC        overhead by using the modulation format subsequent to the        current modulation format in the modulation format list, and        repeating S5 and the steps thereafter until the lightpath        service request is established; and    -   after all the lightpath service requests have been successfully        established, checking all the lightpath service requests in        consideration of the nonlinear interference, recalculating the        OSNR and determining whether it still satisfies the current        modulation format;    -   if the OSNR does not satisfy the current modulation format,        releasing the spectrum resource used by all the lightpaths that        have not been checked starting from the failed lightpath;    -   for the failed service request, lowering the level of the        modulation format used and reallocating the spectrum along the        same shortest path;    -   for the lightpath that has not been checked, reallocating the        spectrum by using the modulation format that has been previously        used and checking whether this lightpath satisfies the        signal-to-noise ratio requirement; and    -   repeating the process above until all the new lightpaths have        been successfully established and all the lightpaths satisfy the        signal-to-noise ratio requirement.

The present invention further discloses a system of OSNR-sensingspectrum allocation with optical channel performance guarantee,including an OSNR construction module, a shortest-path acquisitionmodule, a modulation format sorting module, a spectrum allocation moduleand an OSNR quality evaluation module.

The OSNR construction module is configured to construct an OSNRevaluation model to evaluate the signal transmission quality of thelightpath, the OSNR evaluation model including amplified spontaneousemission noise, nonlinear interference and filter narrowing effect dueto ROADM cascading.

The shortest-path acquisition module is configured to send a lightpathservice request and acquiring the shortest path between the source nodeand the destination node.

The modulation format sorting module is configured to acquire aplurality of modulation formats and corresponding thresholds, sort theplurality of modulation formats according to their spectrum efficienciesin descending order, and acquire a list of the sorted modulationformats.

The spectrum allocation module is configured to calculate the bandwidthrequired by the lightpath service based on the bandwidth demand and FECoverhead by using the modulation format with the highest spectrumefficiency; substitute the bandwidth required by the lightpath serviceinto the OSNR evaluation model and obtain the number of FS actuallyrequired by the service; and allocate the spectrum resource required bythe current service to the shortest path by using the first-fitalgorithm and acquire the center frequency of the current service on thelightpath.

The OSNR quality evaluation module is configured to evaluate the OSNRquality by using a full-spectrum loading strategy, a margin reservationstrategy and a spectrum-dependent strategy respectively to guarantee theoptimum optical channel performance after spectrum allocation.

Hereinafter, the technical solution of the present invention will bedescribed in further detail in combination with a particular embodiment.

I. OSNR Evaluation Model

In the present invention, the signal transmission quality of lightpathis evaluated in terms of OSNR, including three aspects: amplifiedspontaneous emission noise (ASE), nonlinear interference (NLI) andfilter narrowing effect due to ROADM cascading. When the signal in thelightpath passes through a ROADM, which means the signal will passthrough two band-pass filters, the cascaded ROADM filters will cause thefilter bandwidth to decrease. In the present invention, the passband ofthe whole filter is fitted to a high-order Gaussian function so as toabstract the shape of the passband of the cascaded filters. As shown inFIG. 2 , if the signal bandwidth is BW_(s), the 3 dB bandwidth of thefilter is:

$\begin{matrix}{{BW}_{3{dB}} = {{BW}_{s} \times \left\lbrack \frac{T\lbrack{dB}\rbrack}{10 \times \left( {- {\ln z}} \right) \times {\log_{10}(\theta)} \times N_{f}} \right\rbrack^{- \frac{1}{2n}}}} & (1)\end{matrix}$

where T is the insertion loss of the filter in the unit of dB, N_(f) isthe number of cascaded filters, and n is the order of Gaussian function.Also, in order to allow the signals in the lightpath to have the samepower, an optical amplifier such as an Erbium-doped Fiber Amplifier(EDFA) is needed in the present invention to enhance the optical signal,which introduces the ASE noise as shown in FIG. 2 . Thereafter, theoverall signal-to-noise ratio of the lightpath OSNR_(lightpath) can becalculated as:

$\begin{matrix}{{OSNR}_{lightpath} = \frac{P_{in}}{P_{ASE} + P_{NLI}}} & (2)\end{matrix}$

-   -   where P_(in) is the transmit power of the lightpath, P_(ASE) is        the power of the ASE noise, and P_(NLI) is the power of NLI        interference. In the present invention, assuming that each        optical amplifier can exactly compensate for the loss of the        previous signal, P_(ASE) is calculated by the formula:

P _(ASE) =F×h×(G−1)×f _(i) ×B _(i)  (3)

-   -   where F is the noise figure of the optical amplifier, h is the        Planck constant, G is the gain of the optical amplifier, f_(i)        is the center frequency of the signal, and B_(i) is the        bandwidth of the signal.

For the nonlinear interference and assuming additive Gaussian noise,P_(NLI) can be calculated as:

$\begin{matrix} & (4)\end{matrix}$$P_{NLI} = {{\eta \times P_{ch}^{3}} = {P_{ch}^{3} \times \frac{4}{27} \times \frac{\gamma^{2}L_{eff}^{2}B_{i}}{{\pi(a)}^{- 1}\beta_{2}{R_{5}}^{3}}{\sum_{n = 1}^{N_{ch}}\left\{ {{{asinh}\left\lbrack {{\pi^{2}(a)}^{- 1}\beta_{2}{B_{i}\left( {f_{n} - f_{i} + \frac{B_{n}}{2}} \right)}} \right\rbrack} - {{asinh}\left\lbrack {{\pi^{2}(a)}^{- 1}\beta_{2}{B_{i}\left( {f_{n} - f_{i} - \frac{B_{n}}{2}} \right)}} \right\rbrack}} \right\}}}}$

-   -   where

L _(eff)=(1−e ^(−α·L) ^(span) )/α  (5)

γ=2π×n ₂/(λ×A _(eff))  (6)

In the formula (4), “asinh” is the inverse hyperbolic sine function, ais the attenuation coefficient of the optical fiber in the unit of km⁻¹,β₂ is the second order fiber dispersion coefficient, L_(span) is thespan length, span meaning the physical link between two adjacent opticalamplifiers, λ is the wavelength of the signal, n₂ is the nonlinearrefractive index of the optical fiber, and A_(eff) is the effective areaof the optical fiber.

As can be seen from the formula above, the ASE noise is mainly relatedto the attenuation coefficient of the optical fiber and the NLIinterference is mainly related to the effective area of the opticalfiber.

II. OSNR-Sensing Spectrum Allocation

In the present invention, it is necessary to know the center wavelengthand bandwidth of the lightpath in order to calculate the signal-to-noiseratio of the lightpath. Therefore, OSNR calculation is related to thespectrum allocation of each lightpath and different spectrum allocationalgorithms result in different OSNR values. To this end, the routing andspectrum allocation process is to be introduced below in the presentinvention.

In contrast to prior algorithms, the signal-to-noise ratio estimationmodel proposed by the present invention has taken all the damage effectsinto account: ASE noise, NLI interference and bandwidth narrowing effectdue to ROADM filter cascading. The latter two types of damages arerelated to the spectrum information on the link, so it is necessary tocombine signal-to-noise ratio estimation with the spectrum allocationprocess. In contrast, traditional algorithms consider ASE noise as thedamage with essential impact and that the spectrum allocated to thelightpath is irrelevant, which is defective.

The routing and spectrum allocation algorithm according to the presentinvention includes the following steps.

First step: inputting a network topology, a list of a series oflightpath service requests and a set of modulation formats.

Second step: for each request, running a shortest path algorithm to findrouting between the requested source node and destination node.

Third step: first attempting the highest modulation format, themodulation format being PM-64QAM, PM-32QAM, PM-16QAM, PM-8QAM, PM-QPSKand PM-BPSK.

Table 1 shows the spectrum efficiencies and Forward Error Correction(FEC) limits of different modulation formats. It is noted that the FEClimit here is the OSNR threshold corresponding to the modulation format.

TABLE 1 spectrum efficiencies and FEC limits of different modulationformats modulation spectrum efficiency FEC limit format (bit/s/Hz) (dB)PM-BPSK 2 5.32 PM-QPSK 4 8.32 PM-8QAM 6 12.313 PM-16QAM 8 14.98 PM-32QAM10 17.96 PM-64QAM 12 20.88

Based on the bandwidth demand and FEC overhead, the bandwidth requiredby the service is calculated as BW_(s)=N_(s)×f, where f is the bandwidthof each flexible grid (FS) in the network and N, is the number of FSrequired by the service bandwidth.

Fourth step: in consideration of the impact of ROADM filter cascading onsignal bandwidth narrowing, calculating the bandwidth required by thefilter in the current lightpath by the formula (1), and then calculatingthe number of FS actually required by the service as ┌BW_(3dB)/f┐.

Fifth step: allocating the spectrum resource required by the currentservice to the shortest path by using the first fit strategy, whichdetermines the center frequency of the current service on the lightpath.

Sixth step: evaluating the transmission quality OSNR of the lightpath,if the OSNR satisfies the threshold for the current modulation format,establishing a lightpath and ending the allocation process, otherwiseproceeding to the third step and considering the subsequent modulationformat in the list.

III. OSNR Performance Guarantee Strategy

The present invention considers an incremental service scenario whereonly one service request arrives at each time. When a new servicerequest comes up, a new lightpath is set. If a certain lightpath thathas been previously established successfully passes through the samelink and node as the new lightpath, then the spectrum allocated to thenew lightpath will have negative impact on its signal quality. This ismainly due to the Cross Channel Interference (XCI) between thelightpaths. Although Multi-channel Interference (MCI) also existsbetween the plurality of lightpaths, the impact of MCI will be neglectedhere in the present invention as MCI is much weaker than XCI. Meanwhile,the closer the center frequency of the spectrum for the other lightpaththat shares the link or node is to the center frequency of the currentlightpath, the greater the impact from XCI is caused. However, if acertain lightpath previously established does not pass through the samelink or node as the new lightpath, spectrum allocation for the newlightpath will have no impact on the signal quality of this lightpath.Therefore, in order to establish a new lightpath successfully, inaddition to ensuring that the signal-to-noise ratio of the new lightpathsatisfies the threshold requirement, the present invention further needsto consider whether all the lightpaths previously established have beenimpacted and whether they still satisfy the set OSNR threshold.Therefore, the following three strategies are proposed by the presentinvention.

Full-spectrum loading strategy: assuming the case where all the linkshave the worst transmission quality, that is, the whole C band foroptical signal transmission has been occupied, i.e., full-spectrumloading, all the existing XCI impacts have been considered in advance,which ensures that no additional XCI interference will be produced afterestablishment of the new lightpath.

Margin reservation strategy: starting from the first lightpath servicerequest, first the signal-to-noise ratio of the established lightpath iscalculated as OSNR_(current) based on the current spectrum informationon the optical fiber link. Considering the potential XCI effect ofsubsequent lightpath requests, an OSNR margin is reserved in selectingthe modulation format for the current lightpath, that is, it is requiredthat OSNR_(current)−M≥FEC_(limit), where M is the set margin andFEC_(limit) is the OSNR threshold required by the modulation format. Themargin is determined through testing to ensure that all subsequentlightpath requests can be established successfully.

Spectrum-dependent strategy: This strategy is more advanced than the twostrategies mentioned above at the cost of higher calculation complexity.In order to establish the new lightpath LP_(new) successfully, first aspectrum resource is allocated to LP_(new), then in the presentinvention, the list of lightpaths that have been successfullyestablished {LP_(pre)} is checked to confirm whether the lightpaths inthe list that share the link with LP_(new) still satisfy theirrespective OSNR thresholds. If any lightpath fails, then in the presentinvention, starting from the failed lightpath, the spectrum resourcesused by all the lightpaths that have not been checked are released.Then, for the failed service request, in the present invention, thelevel of the modulation format used is lowered, and the spectrum isreallocated along the same route. For the lightpaths that have not beenchecked, the spectra are reallocated to them in the present invention byusing the modulation format that has been previously used and it ischecked to confirm whether they satisfy the signal-to-noise ratiorequirement. In the present invention, this process is repeated untilthe new lightpath has been successfully established and all thelightpaths satisfy their signal-to-noise ratio requirements.

IV. Simulation and Performance Analysis

TABLE 2 Effective Attenuation Dispersion Optical area coefficientcoefficient fiber type [μm²] [dB/km] [ps/nm/km] G.652 83 0.17-0.185 16.40.165 17 G.654.E-A110 110 0.17-0.185 19.2 0.165 20.3 G.654.E-A130 1300.18-0.185 19.2 0.17-0.175 19.1 0.165 19.9

In the present invention, three different types of optical fibers areconsidered as shown in Table 2: G.652, G.654.E-A110 and G.654.E-A130. Inan elastic optical network, to evaluate the performance of the threedifferent types of OSNR guarantee strategies proposed and evaluate howthe attenuation coefficient and the effective area of the optical fiberinfluence the service configuration and performance of the lightpath, anNSFNET network including 14 nodes and 21 links and a USNET networkincluding 24 nodes and 43 links are utilized in the present invention asthe test network of the present invention. In the specific test networkas shown in FIG. 3 , the distance of the link is defined in the unit ofkm. It is assumed here in the present invention that a service demandexists between each node pair, one demand being provided incrementallyeach time. The bandwidth demand for each service is evenly distributedin the range of [120, X]Gb/s, where X is the maximum bandwidth demandbeing set to 700 and 300 in the NSFNET network and the USNET networkrespectively. Assuming that the bandwidth of each FS is 12.5 GHz and theFEC overhead is 25%, with the margin reservation strategy, the marginsof the NSFNET network and the USNET network are set respectively to 1.5dB and 2 dB. The margin set for the USNET network is greater than theone set for the NSFNET network because the USNET network is larger andmore complicated than the NSFNET network. Moreover, the EDFA noisefigure is set to 5.5 dB and the transmit power of each lightpath is 0dBm.

As shown in FIG. 4 , in the present invention, firstly the performancesof the three OSNR performance guarantee strategies are compared. Theparameters of the optical fiber are set as follows: the attenuationcoefficient is 0.185 dB/km and the effective area is 83 m². As thefull-spectrum loading strategy has taken the worst case of all theoptical fiber links into account and the signal-to-noise ratio of eachlightpath is underestimated, the allocated modulation format is of alower level and more spectrum resources are needed. In contrast, thespectrum-dependent strategy only takes interference from the spectrum onthe current lightpath into account, so the actual interference is lowerthan the result from the full-spectrum loading strategy and consequentlyhigher signal-to-noise ratio can be calculated, thereby accomplishingmore effective spectrum resource allocation with the least number of FSbeing used, less than the results from the full-spectrum loadingstrategy by 40.8% and 38.9% for NSFNET and USNET respectively. Althoughthe margin reservation strategy also only takes the interference fromthe spectrum on the current lightpath into account, this strategy usesthe same signal-to-noise ratio penalty for each of the lightpaths. Assuch, this strategy cannot sufficiently take the actual interferencevalue of the current lightpath into account, and needs the intermediatenumber of FS, less than the full-spectrum loading strategy by 28.4% and28.2% for these two networks respectively.

Based on the spectrum-dependent strategy, as shown in FIG. 5 , thepresent invention further evaluates the impacts of the loss and theeffective area of the optical fiber on the configuration and performanceof the lightpath. As can be seen, the number of FS used decreases as theloss of the optical fiber decreases and the effective area thereofincreases, because the former can reduce the ASE noise while the lattercan reduce the NLI interference. When the attenuation coefficient of theoptical fiber decreases, it is found that the number of FS useddecreases almost linearly, which is similar to the result for apoint-to-point system, since this parameter mainly influences the gainof the amplifier and consequently the ASE noise and has little to dowith the spectrum information on the lightpath in the network. Incontrast, as the effective area increases, the number of FS used has thetendency of saturation, particularly from 110 μm² to 130 μm². There aremainly two causes: (1) there is a logarithmic relationship between theeffective area and OSNR; (2) link spectrum not being fully loaded underspectrum-dependent strategy, so XCI improvement diminishes with increaseof the effective area. This result is very useful for optical fiberfabrication, since from the perspective of network performance, thismeans that it is very important to fabricate an optical fiber of thelowest possible attenuation coefficient, but it is not necessary toincrease the effective area once it exceeds 110 μm².

In summary, to evaluate the impacts of the loss and the effective areaof the optical fiber on the service configuration of the lightpath inEON, the present invention proposes a signal-to-noise ratio calculationmodel to evaluate the signal quality of the lightpath. The presentinvention further proposes an OSNR sensing spectrum allocation algorithmand three lightpath allocation strategies with OSNR performanceguarantee. Simulation results show that the spectrum-dependent ONSRperformance guarantee strategy is the most effective and needs the leastnumber of FS and can guarantee the ONSR demand of each lightpath.Researches find that although reducing the optical fiber loss canachieve good service performance, it is not necessary to fabricate anoptical fiber of an effective area over 110 μm².

It should be understood by those skilled in the art that the embodimentsof this application can be provided as a method, a system, or a computerprogram product. Therefore, this application can take the form of anentirely hardware embodiment, an entirely software embodiment or anembodiment combining software and hardware aspects. Furthermore, thisapplication can take the form of a computer program product embodied onone or more computer usable storage media (including but not limited todisk memory, CD-ROM, optical memory, etc.) having computer usableprogram codes embodied therein.

This application is described with reference to flow charts and/or blockdiagrams of methods, devices (systems), and computer program productsaccording to embodiments of this application. It should be understoodthat each flow and/or block in the flow charts and/or block diagrams, aswell as combinations of flows and/or blocks in the flow charts and/orblock diagrams can be implemented by computer program instructions.These computer program instructions can be provided to the processor ofa general-purpose computer, a special-purpose computer, an embeddedprocessor or other programmable data processing devices to produce amachine, so that the instructions executed by the processor of thecomputer or other programmable data processing devices produce means forimplementing the functions specified in one or more flows in the flowchart and/or one or more blocks in the block diagram.

These computer program instructions can also be stored in acomputer-readable memory that can guide a computer or other programmabledata processing devices to operate in a specific way, so that theinstructions stored in the computer-readable memory produce an articleof manufacture including instruction means that implement the functionsspecified in one or more flows in the flow chart and/or one or moreblocks in the block diagram.

These computer program instructions can also be loaded on a computer orother programmable data processing devices, so that a series ofoperation steps are executed on the computer or other programmabledevices to generate computer-implemented processing, so that theinstructions executed on the computer or other programmable devicesprovide steps for implementing the functions specified in one or moreflows in the flow chart and/or one or more blocks in the block diagram.

Obviously, the embodiment described is only an example for clearexplanation and not limitation of the implementation. For those ofordinary skill in the art, other changes or variations in differentforms can be made on the basis of the above description. It is notnecessary and impossible to exhaust all the implementations here.However, the obvious changes or variations derived therefrom are stillwithin the scope of protection created by the present invention.

What is claimed is:
 1. A method of OSNR-sensing spectrum allocation withoptical channel performance guarantee, comprising the steps of: S1:constructing an OSNR evaluation model to evaluate signal transmissionquality of a lightpath, the OSNR evaluation model including amplifiedspontaneous emission noise, nonlinear interference and filter narrowingeffect due to ROADM cascading; S2: sending a lightpath service requestand acquiring the shortest path between a source node and a destinationnode; S3: acquiring a plurality of modulation formats and correspondingthresholds, sorting the plurality of modulation formats according totheir spectrum efficiencies in descending order, and obtaining a list ofthe sorted modulation formats; S4: calculating the bandwidth required bythe lightpath service based on the bandwidth demand and FEC overhead byusing the modulation format with the highest spectrum efficiency; S5:substituting the bandwidth required by the lightpath service into theOSNR evaluation model and obtaining the number of FS actually requiredby the service; and S6: allocating the spectrum resource required by thecurrent service to the shortest path by using a first-fit algorithm, andobtaining the center frequency of the current service on the lightpath.2. The method of OSNR-sensing spectrum allocation with optical channelperformance guarantee of claim 1, wherein the method further comprises,after the step of allocating the spectrum resource required by thecurrent service to the shortest path by using a first-fit algorithm andobtaining the center frequency of the current service on the lightpath:evaluating the OSNR quality by using a full-spectrum loading strategy, amargin reservation strategy and a spectrum-dependent strategyrespectively to guarantee the optimum optical channel performance afterspectrum allocation.
 3. The method of OSNR-sensing spectrum allocationwith optical channel performance guarantee of claim 2, whereinevaluating the OSNR quality by using the full-spectrum loading strategycomprises: evaluating the transmission quality of the lightpath when allthe spectrum resources on the link are occupied and the OSNR performanceis the worst; if the OSNR satisfies the threshold for the currentmodulation format, establishing a lightpath and ending the allocationprocess; otherwise, calculating the bandwidth required by the lightpathservice based on the bandwidth demand and the FEC overhead by using themodulation format subsequent to the current modulation format in themodulation format list, and repeating S5 and the steps thereafter untilthe lightpath service request is established; and after all thelightpath service requests have been successfully established, checkingall the lightpath service requests in consideration of the nonlinearinterference, recalculating the OSNR and determining whether it stillsatisfies the selected modulation format, and if it does not satisfy thecurrent modulation format, blocking this service.
 4. The method ofOSNR-sensing spectrum allocation with optical channel performanceguarantee of claim 2, wherein evaluating the OSNR quality by using themargin reservation strategy comprises: calculating the transmissionquality OSNR of the lightpath based on the center frequency of thecurrent spectrum resource on the fiber link; reserving a margin M; if(OSNR-M) satisfies the threshold for the current modulation format,establishing a lightpath and ending the spectrum allocation process,otherwise, calculating the bandwidth required by the lightpath servicebased on the bandwidth demand and the FEC overhead by using themodulation format subsequent to the current modulation format in themodulation format list, and repeating S5 and the steps thereafter untilthe lightpath service request is established; and after all thelightpath service requests have been successfully established, checkingall the lightpath service requests in consideration of the nonlinearinterference, recalculating the OSNR and determining whether it stillsatisfies the selected modulation format, and if it does not satisfy thecurrent modulation format, blocking this service.
 5. The method ofOSNR-sensing spectrum allocation with optical channel performanceguarantee of claim 2, wherein evaluating the OSNR quality by using thespectrum-dependent strategy comprises: calculating the transmissionquality OSNR of the lightpath based on the center frequency of thecurrent spectrum resource on the fiber link; if the OSNR satisfies thethreshold for the current modulation format, establishing a lightpathand ending the allocation process; otherwise, calculating the bandwidthrequired by the lightpath service based on the bandwidth demand and theFEC overhead by using the modulation format subsequent to the currentmodulation format in the modulation format list, and repeating S5 andthe steps thereafter until the lightpath service request is established;and after all the lightpath service requests have been successfullyestablished, checking all the lightpath service requests inconsideration of the nonlinear interference, recalculating the OSNR anddetermining whether it still satisfies the current modulation format; ifthe OSNR does not satisfy the current modulation format, releasing thespectrum resource used by all the lightpaths that have not been checkedstarting from the failed lightpath; and for the failed service request,lowering the level of the modulation format used and reallocating thespectrum along the same shortest path.
 6. The method of OSNR-sensingspectrum allocation with optical channel performance guarantee of claim5, wherein the method further comprises, after the step of, for thefailed service request, lowering the level of the modulation format usedand reallocating the spectrum along the same shortest path: for alightpath that has not been checked, reallocating the spectrum by usingthe modulation format that has been previously used and checking whetherthis lightpath satisfies the signal-to-noise ratio requirement; andrepeating the process above until all the new lightpaths have beensuccessfully established and all the lightpaths satisfy thesignal-to-noise ratio requirement.
 7. The method of OSNR-sensingspectrum allocation with optical channel performance guarantee of claim1, wherein the step S1 comprises: when the signal bandwidth is BW_(s),the 3 dB bandwidth of the filter is: $\begin{matrix}{{{BW}_{3{dB}} = {{BW}_{s} \times \left\lbrack \frac{T\lbrack{dB}\rbrack}{10 \times \left( {- {\ln z}} \right) \times {\log_{10}(\theta)} \times N_{f}} \right\rbrack^{- \frac{1}{2n}}}},} & (1)\end{matrix}$ where T is the insertion loss of the filter in the unit ofdB, N_(f) is the number of cascaded filters, and n is the order ofGaussian function; the overall signal-to-noise ratio of the lightpathOSNR_(lightpath) is $\begin{matrix}{{{OSNR}_{lightpath} = \frac{P_{in}}{P_{ASE} + P_{NLI}}},} & (2)\end{matrix}$ where P_(in) is the transmit power of the lightpath,P_(ASE) is the power of the ASE noise, and P_(NLI) is the power of NLIinterference; in the case where each optical amplifier can exactlycompensate for the loss of the previous signal, P_(ASE) is calculated bythe formula:P _(ASE) =F×h×(G−1)×f _(i) ×B _(i)  (3) where F is the noise figure ofthe optical amplifier, h is the Planck constant, G is the gain of theoptical amplifier, f_(i) is the center frequency of the signal, andB_(i) is the bandwidth of the signal; for the nonlinear interference andassuming additive Gaussian noise, P_(NLI) can be calculated as:$\begin{matrix} & (4)\end{matrix}$$P_{NLI} = {{\eta \times P_{ch}^{3}} = {P_{ch}^{3} \times \frac{4}{27} \times \frac{\gamma^{2}L_{eff}^{2}B_{i}}{{\pi(a)}^{- 1}\beta_{2}{R_{5}}^{3}}{\sum_{n = 1}^{N_{ch}}\left\{ {{{asinh}\left\lbrack {{\pi^{2}(a)}^{- 1}\beta_{2}{B_{i}\left( {f_{n} - f_{i} + \frac{B_{n}}{2}} \right)}} \right\rbrack} - {{asinh}\left\lbrack {{\pi^{2}(a)}^{- 1}\beta_{2}{B_{i}\left( {f_{n} - f_{i} - \frac{B_{n}}{2}} \right)}} \right\rbrack}} \right\}}}}$where L_(eff)=(1−e^(−α·L) _(span))/α·γ=2π×n₂/(λ×A_(eff)), “asinh” is theinverse hyperbolic sine function, α is the attenuation coefficient ofthe optical fiber, β₂ is the second order fiber dispersion coefficient,L_(span) is the span length, span meaning the physical link between twoadjacent optical amplifiers, λ is the wavelength of the signal, n₂ isthe nonlinear refractive index of the optical fiber, and A_(eff) is theeffective area of the optical fiber.
 8. The method of OSNR-sensingspectrum allocation with optical channel performance guarantee of claim1, wherein the plurality of modulation formats in the step S3 comprises:PM-64QAM, PM-32QAM, PM-16QAM, PM-8QAM, PM-QPSK and PM-BPSK.
 9. A systemof OSNR-sensing spectrum allocation with optical channel performanceguarantee, comprising: an OSNR construction module configured toconstruct an OSNR evaluation model to evaluate the signal transmissionquality of the lightpath, the OSNR evaluation model including amplifiedspontaneous emission noise, nonlinear interference and filter narrowingeffect due to ROADM cascading; a shortest-path acquisition moduleconfigured to send a lightpath service request and acquire the shortestpath between a source node and a destination node; a modulation formatsorting module configured to acquire a plurality of modulation formatsand corresponding thresholds, sort the plurality of modulation formatsaccording to their spectrum efficiencies in descending order, andacquire a list of the sorted modulation formats; and a spectrumallocation module configured to calculate the bandwidth required by thelightpath service based on the bandwidth demand and FEC overhead byusing the modulation format with the highest spectrum efficiency;substitute the bandwidth required by the lightpath service into the OSNRevaluation model and obtain the number of FS actually required by theservice; and allocate the spectrum resource required by the currentservice to the shortest path by using a first-fit algorithm and acquirethe center frequency of the current service on the lightpath.
 10. Thesystem of OSNR-sensing spectrum allocation with optical channelperformance guarantee of claim 9, wherein the system further comprises:an OSNR quality evaluation module configured to evaluate the OSNRquality by using a full-spectrum loading strategy, a margin reservationstrategy and a spectrum-dependent strategy respectively to guarantee theoptimum optical channel performance after spectrum allocation.